A finger follower (lever) is a transmission element of a valve train, for example, of a piston-type internal combustion engine. This finger follower allows the lift movement of a cam that is produced by the rotation of a camshaft to be transmitted to a lift valve, which is axially opened to exchange the load for the reset force of a valve spring. For this purpose one end of the finger follower (lever) is mounted in an articulated manner on a housing-sided support element; and the opposite end of said finger follower rests against the stem end of the assigned lift valve. Between its ends the side of the finger follower that faces away from the support element and the lift valve makes contact with the assigned cam of the camshaft. As a result, the lift that is predefined by the contour of the cam and has increased in accordance with the effective lever ratio is transmitted to the stem end of the lift valve. In order to obtain a valve train with minimum friction, the finger follower is often designed as a so-called roller-type finger follower, that is, provided with a roller, which is mounted in a rotatable manner and makes contact with the assigned cam of the camshaft.
The present invention is based on a finger follower (lever) comprising a lever body that is designed preferably as a pressed or punched component made of sheet metal, but it can also be fabricated as a casting with subsequent mechanical finishing. The support element-sided end of the lever body has a spherical cap-shaped bearing cup for an articulated mounting on a bearing pin of a housing-sided support element, said bearing pin terminating as a spherical cap. The support element can be, for example, a piston, which is mounted in an axially moveable manner in a vertical hole of the cylinder head of the piston-type internal combustion engine under discussion. In order to compensate for any temperature induced valve play that occurs between the cam of the camshaft and the stem end of the respective lift valve, said piston can be loaded with pressure oil on an inner piston surface.
Since the finger follower and the support element form a module, in which they are adapted to each other, these components are often connected together in a loss-proof manner by means of a retaining clamp. In this case the articulated mounting should not be adversely affected by additional frictional and flexural losses. For this purpose the retaining clamp is usually attached to the respective base web of the lever body in such a way that it engages laterally with an annular groove of the bearing pin without impeding the ability of the finger follower to swivel relative to the support element in the operating direction.
DE 196 17 523 C2 describes a number of embodiments of such retaining clamps, which are designed to some extent as sheet metal retaining clamps, wire retaining brackets and as plastic retaining brackets. One preferred embodiment of a sheet metal retaining clamp has a U-shaped cross section with bifurcated arms of an inner leg and with a closed outer leg. The sheet metal retaining clamp is pushed from the outside in the longitudinal direction onto the base web of the lever body exhibiting the bearing cup and is locked on said base web with the end-sided retaining lug. In the assembled state the bifurcated arms of the inner leg engage laterally with the annular groove of the bearing pin, so that the finger follower and the support element are connected together in a form locking manner with play.
A preferred embodiment of a wire retaining bracket according to this prior art has two parallel bracket arms, which in the assembled state engage laterally with the annular groove of the bearing pin and are externally connected together by means of a connecting bracket. Both the free inner ends and the outer ends of the bracket arms that are connected together by the connecting bracket are bent upwards at right angles and are provided with a retaining lug formed thereon, so that it is possible to push the wire retaining bracket on, starting from the bearing side, and to fasten it in a form and force locking manner to the associated base web of the lever body.
The figures in DE 10 2006 052 821 A1, which presents a specific design of the valve-sided end of a lever body of a follower finger (lever) designed as a pressed and punched component made of sheet metal, show a sheet metal retaining clamp, which is configured in a manner similar to the sheet metal retaining clamp known from DE 196 17 523 C2. The distinction between the former and the sheet metal retaining clamp of the present invention lies in the fact that its inner leg has a connecting web, which is formed in the manner of a retaining clip and which connects the lateral arms. As a result, the inner leg of the sheet metal retaining clamp is designed as a closed sheet metal spring frame with higher flexural and torsional strength.
The figures in DE 10 2007 006 695 A1, which proposes another design of the valve-sided end of a lever body of a follower finger (lever) designed as a pressed and punched component made of sheet metal, show a sheet metal retaining clamp, which practically consists of only one sheet metal spring frame, which is arranged on the bearing side on the respective base web of the lever body and corresponds to the inner leg of the sheet metal retaining clamp known from DE 10 2006 052 821 A1. The connecting webs of the lateral arms are bent upwards at right angles in a manner similar to the wire retaining bracket known from DE 196 17 523 C2 and is formed into a retaining clip on the end side. This design makes it possible to slide the sheet metal retaining clamp starting on, from the bearing side, and to lock it on the respective base web of the lever body.
Experience with conventional valve trains has shown that the prior art retaining clamps are totally adequate for securing in a loss-proof manner the finger follower at the support element in the course of assembly and also in the event of malfunctions in operation, for example due to a faulty supply of oil to the hydraulic system. If, however, a finger follower and the associated roller are designed relatively narrow and are loaded with a transverse force, there is the risk that the lever body will tilt sideways and slip off the support element. This applies, in particular, to variable valve trains with cam shifting systems, like the Audi valve lift system (AVS) and the cam shifting system (INA), where, instead of cams, which are rigidly connected to the camshaft, a cam body with two or three different, axially adjacent cams are provided. Each cam body is mounted in a rotationally rigid and axially displaceable manner on the cam shaft by means of a drive gear and is axially displaceable with the assigned roller by means of a link motion, in order to switch to another cam in the contact region of the cam heel. In this case the lever body and the rollers are designed relatively narrow because of the limited installation space and are loaded with a transverse force when changing the active cam.